Ignore unmatched properties during deserialization

[tomjschneider]

Description

This change updates the deserialization of the TestPlanDefinition so that any unmatched properties will be ignored, rather than throwing an exception. This should help with future supportability for the YAML files, so that the TestPlanDefinition object can be updated independently from the actual files.

I also fixed a few very minor things:

• Moved the creation of the output directory info a bit earlier. Today, if you run Test Engine with a YAML file that is not present, you don't get a helpful error message.
• Updated the README to be more accurate for setup.

Checklist

• [x] The code change is covered by unit tests. I have added tests that prove my fix is effective or that my feature works
• [x] I have performed end-to-end test locally.
• [x] New and existing unit tests pass locally with my changes
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I used clear names for everything
• [x] I have performed a self-review of my own code

[github-actions[bot]]

Package	Line Rate	Branch Rate	Complexity	Health
Microsoft.PowerApps.TestEngine	91%	88%	826	✔
Summary	91% (2206 / 2435)	88% (500 / 566)	826	✔

Minimum allowed line rate is 85%

[tomjschneider]

After discussion with the team, we don't want to ignore unmatched properties. Closing this PR.